LOS ANGELES
— An infection of the uterine cavity during pregnancy combined with
premature birth doubles the risk that an African American child will
develop asthma, researchers have found. The combination also increases
risk for some other ethnicities, though less severely.

About 8 percent of pregnancies are marked by such
bacterial infections, called chorioamnionitis, but it is not yet clear
what proportion of asthma is induced by them, said the lead author of
the study, Dr. Darios Getahun of Kaiser Permanente’s Department of Research and Evaluation in Pasadena, Calif.
Nor is it clear whether the duration of the infection influences the
risk and why different ethnicities respond differently, he said.

But blacks have about a 25 percent higher incidence
of asthma and the new findings could account for a significant portion
of that increase. Asthma incidence is also higher in American Indian
and Alaskan Native populations, but the researchers were not able to
examine that association.

About 14 percent of American children suffer from
asthma, an inflammation of the airways that is marked by wheezing,
shortness of breath, chest tightening and coughing. About half of such
cases are believed to be of genetic origin, but the cause of the rest
has been a mystery.

Many studies have looked at the risk of asthma
related to Caesarean sections, exposure to antibiotics and other
factors related to delivery, Getahun said. “We were thinking that it
was really exposure (in the uterus) that may predispose children to
asthma later in life.”

Getahun and his colleagues took advantage of the extensive electronic medical records of Kaiser’s Southern California Medical Group,
studying 397,852 births between 1991 and 2007. They reported Monday in
the journal Archives of Pediatric and Adolescent Medicine that
chorioamnionitis had no apparent effect on the rate of asthma when the
fetuses were carried full term.

But when the mother suffered from the infection and
gave birth prematurely, the risk of asthma developing before the age of
8 was 98 percent higher in black children, 70 percent higher in Latino
children and 66 percent higher in Caucasian children. No increased risk
was observed, however, for children of Asian or Pacific Islander
descent.

Getahun speculated that the infections — which can
be caused by a broad variety of bacteria — cause inflammation of the
fetal lungs, either injuring the lungs or predisposing them to react
more severely to future environmental insults.

The team now is planning to look for markers that
would identify chorioamnionitis at an earlier stage and to explore why
the infections affect different races differently.

Chorioamnionitis is marked by a fever above 100.4
degrees F. in the absence of any obvious source of infection, and may
also be manifested as increased maternal or fetal heart rate, uterine
tenderness, foul-smelling amniotic fluid and increased white blood cell
counts.